Peptides have conventionally been employed for the treatment or the like of various diseases. For example, calcitonin, insulin, interferon and erythropoietin are used for the improvement of osteoporosis and pains associated with osteoporosis and the treatment of diseases such as hypercalcemia, for the treatment of diseases such as diabetes, for the treatment of diseases such as hepatitis and renal carcinoma, and for the treatment of diseases such as anemia, respectively.
As an administration method of peptides, administration by injection is usual because of the difficulty in having them absorbed through the digestive tract. However, this injection-reliant administration is not an administration method which permits self-administration by a patient, so that regular outpatient treatment is required. It also involves the problem of administration being accompanied by painful discomfort.
On the other hand, from the standpoint of economy, oral administration is accompanied by a problem because the absorption rate of a peptide through the digestive tract is low and moreover, the peptide is subjected to decomposition, first-pass effect and the like by proteinases and hence, the peptide has to be administered in a very large quantity to have it absorbed in an effective amount through the digestive tract.
Concerning the administration form of peptides, a great deal of research is now under way to overcome the above-described problems. Intranasal sprays containing peptides as effective ingredients have already been developed in Europe. However, they are accompanied by problems such as insufficient absorption of the peptides and are not satisfactory.
With a view to increasing the absorbability of peptides, it has heretofore been attempted to formulate them into preparations with the addition of a bile acid salt or a surfactant [Japanese Patent Application Laid-Open (Kokai) No. SHO 59-130820, Japanese Patent Application Laid-Open (Kokai) No. SHO 59-89619, and Japanese Patent Application Laid-Open (Kokai) No. SHO 63-39822] or to use a proteinase inhibitor for promoting permucosal absorption [J. Pharmacobiodin. 14(2), S4, 1991, and Japanese Patent Application Laid-Open (Kokai) No. HEI 3-48627). The absorption enhancers employed in these preparations are all accompanied by one or more safety problems such as excessively strong mucosal irritation, so that none of them have been put into practice.
From the foregoing circumstances, there is an outstanding desire for the development of a preparation which is free of the above-described problems .